1. Field of the Invention
The present invention relates to a backlight unit for a liquid crystal display (LCD), and more particularly to a backlight unit structure for a liquid crystal display having a blink backlight structure provided with a reflection plate to allow for improvement of a response time and accomplishment of a high luminance.
2. Description of the Prior Art
In order to improve a response time in an LCD, a technique using a high-speed response liquid crystal has been employed in general. In addition, the response time may be further improved by utilizing the panel structures such as a VA (Vertical Alignment) panel structure, an IPS (In Plane Switch) panel structure, an OCB (Optically Compensated Bend) panel structure and so forth, rather than a typical TN (Twisted Nematic) panel structure. Yet another technique of improving the response time may be to select a driving method such as a CCD driving method over others.
Even though the above-mentioned various techniques have been used to improve the response time, it has been impossible to acquire the same response time as a CRT (Cathode Ray Tube).
This results from a display principle of the CRT, which is based on an impulse light emission system. That is, the CRT is displayed by emitting light once (2-3 ms) a frame (16.7 ms, 60 Hz).
However, because the LCD emits light in succession (16.7 ms) during one frame, a blur phenomenon is generated while the LCD is displayed, unlike the CRT. In particular, in the case of a moving picture, a serious mismatch phenomenon wherein image signals are mismatched with the eyes of a user is generated from the LCD. This mismatch phenomenon is a common phenomenon found not only in an LCD but also in display devices using a method of steadily emitting light, such as a plasma display panel (PDP) and an electroluminescence (EL) display.
As shown in FIGS. 1a and 1b, an impulse system is realized by providing a plurality of lamps 13 in a backlight module 11 disposed under a display panel 15, and then by performing a sequential turning on/off according to a principle similar to that in a CRT display.
Here, to obtain a satisfactory display image quality, the sequential turning on/off is synchronized with a gate signal at the same time. In other words, as in FIG. 2, lamps 13 located under a gate line become on-state when the gate signal is applied to the gate line, while the lamps 13 become off-state when the gate signal is not applied to the gate line. That is, the on-state of the lamps 13 is gradually shifted from the upper side of the display to the lower side thereof.
According to research data of Hitachi Inc., when the sequential turning on/off mode is used in a blink backlight system having six lamps, a luminance is reduced at 16% compared with a system in which the lamps are continuously turned on. When a duty time of the lamp is set to 60%, luminance of 60% can be obtained.
As the duty time becomes shorter, a trade-off relationship ensues, in which a moving picture becomes clearer but the luminance becomes reduced. The research data of Hitachi Ltd. reports that a minimum duty time for reducing the blur phenomenon in a moving picture of an LCD is 70%.
Further, as a tube current of a typical luminous body (CFL (Color Cathode Fluorescent Lamp)) is growing high, a temperature of the lamp is increased, and thus an efficiency of the luminance is decreased.
In the blink backlight system, because the off-state of the lamp prevents the temperature of the lamp from increasing, there is a room to increase the tube current compared with the lamp in a steady on-state, so that the luminance can be increased.